Mounting structure for electric oil pump

ABSTRACT

A mounting structure for electric oil pump is provided to allow the electric oil pump to be mounted without through a communication pipe. The electric oil pump includes a pump unit having an inscribed gear pump, and a motor unit disposed adjacent to the pump unit and having a sensorless brushless DC motor for rotating the inscribed gear pump. A transmission accommodates the electric oil pump and includes a transmission case having an oil pan. The electric oil pump is attached to the transmission case with at least a through hole for supplying working oil to the pump unit being submerged in the working oil reserved in the oil pan.

TECHNICAL FILED

The present invention relates to a mounting structure for electric oilpump used for a vehicle such as a motorcar.

BACKGROUND ART

Some kinds of vehicles including motorcars have recently been proposedtaking into account of environmental problems, which vehicles include afunction for turning off an engine during a short period of time whenthe vehicle is temporarily stopped at an intersection, for example, toreduce exhaust gas or gasoline consumption. Although the engine is notactuated when such a function is activated, it is still required in thatcase to maintain oil pressure for a transmission. Thus, the oil pressureis maintained with use of an electric oil pump that can be driven tosupply and circulate oil (an example of “working oil”) while the enginestops.

The electric oil pump is typically attached to a wall surface of anoutside (outer wall) of a transmission case. The electric oil pumpincludes an oil intake opening connected to an oil pan reserving oil viaa communication pipe with a distal end of the communication pipe beingsubmerged in oil. As the electric oil pump is rotated to generatenegative pressure, reserved oil is drawn up through the communicationpipe, passes through the interior of the communication pipe, and thenflows into the interior of the electric oil pump via the intake opening.The oil is then pressurized within the pump to be pressure fed to theinterior of the transmission case through a discharge opening forcirculation. The electric oil pump is driven by a motor forming a motorunit.

Patent Literature 1 discloses a structure for installing an electric oilpump, in which the electric oil pump is disposed in a lower part of anouter surface of a transmission case to draw up oil from an oilreservoir (oil pan) in the transmission case via an intake oil passage(communication pipe) and supply the oil to the transmission.

CITATION LIST

-   Patent Literature 1: Japanese Unexamined Patent Application    Publication No. 2010-276035

SUMMARY OF INVENTION Technical Problem

When oil flows through the communication pipe, resistance caused byfriction between oil and an inner wall of the communication pipe(“piping resistance” hereinafter) is generated. Thus, when oil issupplied to the electric oil pump through the communication pipe, it isrequired to determine output of power of the motor driving the electricoil pump based on the piping resistance in addition to viscosityresistance of the oil per se. As a result, greater output of power forthe motor is required than in a case where only the oil viscosityresistance, which is essentially required, should be taken into account.This requires a larger motor. Using a large motor leads not only toincreased cost but also to a large accommodating space for increasedvolume and weight of the motor, which is disadvantageous when mounted toan motorcar.

The piping resistance is proportional to the oil viscosity. Decrease inoil temperature increases the oil viscosity and thus the pipingresistance, as a result which the motor is subject to increased loadwhen started up, in particular, and might not be able to start up in theworst case.

Thus, there is room for further improvement in providing the electricoil pump using the communication pipe.

The electric oil pump is typically attached to and project from theouter wall of the transmission case. How large space there is around thetransmission depends on a type of vehicle. If the vehicle cannot secureenough space for accommodating the projecting part of the electric oilpump, such a pump cannot be attached to the transmission case.

Further, the electric oil pump typically has an assembled constructionin which a motor unit is fastened and screwed to a pump housing of apump unit and a pump cover to form an integral structure. On the otherhand, the electric oil pump is attached and fastened to the outer wallof the transmission through further screws. This means that twoscrew-fastening steps are required, which might result in increased workprocesses and thus increased cost.

Moreover, with the above arrangement of the electric oil pump, oil mightleak from boundaries between the components screwed to each other, i.e.,boundaries between the motor unit and the pump housing or between thepump housing and the pump cover. Oil leakage from the electric oil pumpattached to the outside of the transmission case would result in aserious problem. To prevent such oil leakage, annual seals need to beprovided to the boundaries between the above components, which alsoleads to increased cost.

Thus, there is room for further improvement in attaching the electricoil pump to the outside of the transmission case as well.

Under the circumstances, it has been desired that the electric oil pumpbe provided without using any communication pipe. It has also beendesired that the electric oil pump be mounted regardless of whetherspace around the transmission case is small or large.

Solution to Problem

To achieve the above objects, the present invention is characterized bya mounting structure for electric oil pump including an electric oilpump and a transmission case, in which the electric oil pump includes apump unit having a pump, a motor unit disposed adjacent to the pump unitand including a motor for rotating the pump, a motor case for housing atleast part of the motor unit, and an intake opening formed in the motorcase or the pump unit for supplying working oil to the pump unit, andthe transmission case includes an oil pan for housing the electric oilpump. The electric oil pump is attached to the transmission case with atleast the intake opening being submerged in the working oil reserved inthe oil pan.

With the above arrangement, the working oil is drawn up directly fromthe intake opening without needing to drawn up the oil through thecommunication pipe as in the conventional structure, as a result ofwhich no piping resistance is generated. Thus, output of power of themotor can be determined only based on viscosity resistance of oil. Thismakes the motor compact to provide a more inexpensive electric oil pump.

It is preferable in the mounting structure according to the presentinvention that the electric oil pump further comprises a driver unit forcontrolling rotating speed of the motor, and the driver unit is disposedoutside the transmission case and located opposite to the motor unitacross the transmission case.

With the above arrangement, no working oil is adhered to the driverunit, and thus no malfunction of the driver unit would be caused by oiladhesion. Additionally, the driver unit is provided outside thetransmission case, which facilitates heat radiation from the driverunit.

It is preferable in the mounting structure according to the presentinvention that a strainer screen is attached to the intake opening.

In the conventional arrangement in which the working oil is drawn upthrough the communication pipe, the strainer screen is attached to adistal end of the communication pipe submerged in the oil pan, andfurther an oil filter that is coarser than the strainer screen isattached to a boundary between an intake passage and the communicationpipe of the electric oil pump. In contrast, according to the mountingstructure of the present invention in which the electric oil pump issubmerged in oil when attached to the transmission case, it is onlyrequired that the strainer screen is attached to the intake opening toremove foreign substances from oil, which dispenses with a coarser oilfilter. As a result, further cost reduction for the electric oil pump isachieved.

It is preferable in the mounting structure according to the presentinvention that the pump unit includes an inner rotor, an outer rotormeshed with the inner rotor to rotate with rotation of the inner rotor,and a housing for accommodating the inner rotor and the outer rotor, theinner rotor and the outer rotor are made of different materials fromeach other, and the outer rotor is made of a material having a linearexpansion coefficient greater than that of a material forming thehousing.

In normal room temperature, a clearance between a thickness of the outerrotor and a depth of the housing and a clearance between an outerdiameter of the outer rotor and an inner diameter of the housing areboth larger than regular clearances provided in a typical pump. Withsuch an arrangement, intake working oil leaks between pump chambersdefined in the pump, which results in unsatisfactory pressurization ofworking oil in the pump. However, as the electric oil pump is started upto increase its temperature, both the housing and the outer rotorthermally expand. Since the outer rotor is made of a material having alinear expansion coefficient greater than that of a material forming thehousing, the outer rotor expands greater than the housing. As a result,the clearances become small. These clearances are set to proper valuesfor the electric oil pump when operated in normal condition. Thus, suchan arrangement can reduce oil leakage between the pump chambers andimprove volume efficiency of the electric oil pump.

It is preferable in the mounting structure according to the presentinvention that the electric oil pump further includes a driver unit forcontrolling rotating speed of the motor. The driver unit receives afirst signal which is outputted from the motor and corresponds to therotating speed of the motor, and outputs the signal to an upper ECU as asecond signal. The ECU determines whether the rotating speed of themotor falls within a normal range. The driver unit corrects the receivedfirst signal to a signal falling within the normal range when the firstsignal indicates that the motor rotates with a rotating speed outsidethe normal range and within a predetermined range of rotating speedoutside the normal range, and outputs the corrected signal to the ECU asthe second signal.

With the electric oil pump being driven, the first signal relating tothe rotating speed transmitted from the motor is detected at the driverunit, converted to the second signal which is a pulse signal having afrequency corresponding to the rotating speed, and then transmitted tothe upper ECU. In this, however, oil pressure required for supplyingworking oil to the transmission varies depending on vehicle types orenvironmental conditions such as surrounding temperature. In many cases,however, a range of normal rotation in the ECU is fixedly determinedregardless of these conditions. Therefore, even if the electric oil pumpsupplies required oil pressure, an unusual rotation state is detectedwhen the motor rotates with a rotating speed outside the normal range.According to the present invention, the driver unit corrects thereceived first signal to a signal falling within the normal range whenthe first signal indicates that the motor rotates with a rotating speedoutside the normal range and within a predetermined range of rotatingspeed outside the normal range, and outputs the corrected signal to theECU as the second signal. Performing such control of rotating speed ofthe motor allows the ECU to determine that the motor rotates withrotating speed within the normal range while feeding required oilpressure to the transmission without increasing the output of power ofthe motor.

It is preferable in the mounting structure according to the presentinvention that the first signal is corrected when the first signalindicates lower rotating speed than the normal range.

If the received first signal indicates that the rotating speed of themotor is higher than the normal range, there is a possibility that themotor is running idle. Such a condition is absolutely abnormal and thus,the driver unit must not generate a corrected signal as a second signal.However, when the rotating speed is lower than the normal range, theelectric oil pump supplies required oil pressure in most cases in spiteof low speed rotation of the motor. In view of this, the driver unit isconfigured to correct the first signal when the rotating speed is lowerthan the normal range to transmit the second signal indicating thenormal range of rotating speed to the ECU. Such control allows the ECUto determine that the motor rotates with rotating speed within thenormal range while feeding required oil pressure to the transmissionwithout increasing the output of power of the motor.

It is preferable in the mounting structure according to the presentinvention that the intake opening is provided opposite to the pump unitacross the motor unit, and the working oil flows within the motor unitand is supplied to the pump unit.

With the above arrangement in which the pump has a flow passagestructure to draw up oil flowing within the motor unit, the pump candraw up oil that has high temperature and low viscosity due to heatgeneration caused by actuation of the motor. This allows the pump tosmoothly rotate. Additionally, the oil contrariwise absorbs the heatgenerated by the motor when the oil communicates through the interior ofthe motor unit. Thus, the motor is not excessively heated and therotation efficiency of the motor is not declined.

It is preferable in the mounting structure according to the presentinvention that the pump unit includes a pump housing and a pump cover,which are disposed adjacent to each other, the pump housing and themotor unit are integrally attached to an inner wall of the transmissioncase, and the pump cover is formed in the transmission case.

With the above arrangement in which the pump housing and the motor unit,which cover most of the volume of the electric oil pump, are attached tothe inner wall of the transmission case inside the transmission, theelectric oil pump does not protrude outward from the transmission. Thus,the electric oil pump can be mounted regardless of whether space aroundthe transmission case is small or large, which means, regardless ofvehicle types.

It is preferable in the mounting structure according to the presentinvention that a recess is formed in an outer wall of the transmissioncase, and the driver unit is housed in the recess.

With the above arrangement in which the driver unit also does notprotrude outward from the transmission, the electric oil pump can bemounted regardless of whether space around the transmission case issmall or large, which means that the pump can be mounted in vehicles ofa wider range of types.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view of a mounting structure for electric oil pumpaccording to a first embodiment;

FIG. 2A is an enlarged view of a part IIa in FIG. 1;

FIG. 2B is a sectional view taken on line IIb-IIb in FIG. 2A;

FIG. 3 is a descriptive view of control of rotating speed of asensorless brushless DC motor by a driver unit;

FIG. 4 is a sectional view of the mounting structure for electric oilpump according to a variation of the first embodiment; and

FIG. 5 is a sectional view of the mounting structure for electric oilpump according to a second embodiment.

DESCRIPTION OF EMBODIMENTS 1. First Embodiment [Construction of ElectricOil Pump] (1) Structure of Pump Unit

An electric oil pump according to a first embodiment of the presentinvention will be described hereinafter in detail in reference to theaccompanying drawings. Referring to FIG. 1, the electric oil pump 1according to the current embodiment is formed of a pump unit 10 and amotor unit 30. The pump unit 10 includes a pump housing 11, an inscribedgear pump 14, and a pump cover 40. The pump housing 11 and the pumpcover 40 are examples of “housing,” and the inscribed gear pump 14 is anexample of “pump”.

As illustrated in FIG. 1, the pump housing 11 includes a bottomedreceiving recess 12 formed at one end face thereof. The receiving recess12 is cylindrical in external configuration and is circular in section.An intake port 41 a and a discharge port 42 a are formed in a bottomsurface of the receiving recess 12. An intake passage 43, which is ahole extending through the pump housing 11, is formed in a bottomsurface of the intake port 41 a. A shaft receiving hole 19 is formed ina position that is eccentric from an axis of the receiving recess 12 ofthe pump housing 11. A rotary shaft 13 extends through the shaftreceiving hole 19 and an inner rotor 15 of the inscribed gear pump 14.The rotary shaft 13 is rotatably supported in the shaft receiving hole19 to be rotatable in unison with the inner rotor 15 about a commonrotation axis X.

The inscribed gear pump 14 is housed in the receiving recess 12 andincludes an outer rotor 16 in addition to the inner rotor 15. Referringto FIG. 2B, the inscribed gear pump 14 is structured such that outerteeth formed in the inner rotor 15 are meshed with inner teeth formed inthe outer rotor 16. With rotation of the inner rotor 15, the outer rotor16 rotates around the inner rotor 15. A number of pump chambers 17 areformed between the teeth of the inner rotor 15 and the teeth of theouter rotor 16. The capacity of each pump chamber increases or decreaseswith the rotation of the rotors.

The pump cover 40 is disposed adjacent to the pump housing 11 having thesame outer diameter as that of the pump housing 11. The pump cover 40and the pump housing 11 are fastened to each other through anunillustrated screw to form an integral unit. The pump cover 40 has anintake port 41 b provided opposite to the intake port 41 a across thereceiving recess 12, and a discharge port 42 b provided opposite to thedischarge port 42 a across the receiving recess 12. A discharge passage44 extends outward from the discharge port 42 b.

The intake ports 41 a and 41 b are crescent grooves as shown in FIG. 2Bto communicate with the pump chambers 17 along a range in which thecapacities of the pump chambers 17 of the inscribed gear pump 14increase. Likewise, the discharge ports 42 a and 42 b are also crescentgrooves as shown in FIG. 2B to communicate with the pump chambers 17along a range in which the capacities of the pump chambers 17 of theinscribed gear pump 14 decrease.

According to the current embodiment, the inner rotor 15 and the outerrotor 16 are made of different materials, in which the outer rotor 16 ismade of a material having a linear expansion coefficient greater thanthat of a material forming the pump housing 11 and the pump cover 40. Asan example of material combinations, the inner rotor 15 is made of aniron sintered material, the outer rotor 16 is made of aluminum or analuminum alloy, and the pump housing 11 and the pump cover 40 are madeof iron. In another example, the inner rotor 15 is made of an ironsintered material, the outer rotor 16 is made of resin, and the pumphousing 11 and the pump cover 40 are made of aluminum or an aluminumalloy.

Referring to FIG. 2A, the receiving recess 12 and the pump cover 40define an accommodating space therebetween for the inscribed gear pump14. In normal room temperature, the accommodating space has a dimensionalong the rotation axis X greater than a thickness of the outer rotor 16along the rotation axis X, and a radial dimension greater than an outerdiameter of the outer rotor 16. More particularly, a clearance 12 aalong the rotation axis X and a radial clearance 12 b are definedbetween the accommodating space and the outer rotor 16. In normal roomtemperature, the clearance 12 a and the radial clearance 12 b are largerthan a regular clearance provided in a typical pump, and dimensioned toallow intake oil (an example of “working oil”) to leak between the pumpchambers 17 and prevent the oil from being pressurized sufficiently.

Although there might be concern that volume efficiency in the electricoil pump 1 will be lowered in such a condition, staring up the electricoil pump 1 increases temperature of the inscribed gear pump 14 due toheat generation from the motor unit 30 or increase in temperature of oilcaused by the start-up operation, as a result of which the clearances 12a and 12 b become small in use. With the use of the pump in such acondition, no practical problem would arise with the clearances 12 a and12 b being larger in normal room temperature. On the contrary, suchclearances 12 a and 12 b can reduce friction between the outer rotor 16and the pump housing 11 or the pump cover 40. This would avoid increasein load applied to the electric oil pump 1 in normal room temperature inwhich oil viscosity is greater than in higher temperature, and thuswould not mar the start-up performance of the electric oil pump 1.Although the oil viscosity further increases at lower temperature thanthe normal room temperature, the clearances 12 a and 12 b also furtherincrease, as a result of which the start-up performance of the electricoil pump 1 is maintained. With such an arrangement in which the outerrotor 16 is made of a material having a greater linear expansioncoefficient than that of a material of the pump housing 11 or the pumpcover 40, the electric oil pump 1 can start up in a stable mannerregardless of start-up surrounding temperature.

Next, how the clearances 12 a and 12 b decrease when the electric oilpump 1 is actually actuated will be described hereinafter in moredetail. As the electric oil pump 1 is started up to increase itstemperature, all of the pump housing 11, the pump cover 40, and theouter rotor 16 thermally expand. In this time, the outer rotor 16expands greater than the pump housing 11 and the pump cover 40 becausethe outer rotor 16 is made of a material having a greater linearexpansion coefficient than that of a material of the pump housing 11 orthe pump cover 40, as a result of which the clearances 12 a and 12 bbecome small. The clearances 12 a and 12 b are set to proper values intemperature at which the electric oil pump 1 is operated in normalcondition. This reduces oil leakage between the pump chambers 17 andimproves the volume efficiency of the electric oil pump 1.

(2) Structure of Motor

As illustrated in FIG. 1, the motor unit 30 is disposed adjacent to thepump unit 10. The motor unit 30 includes a sensorless brushless DC motor31. The sensorless brushless DC motor 31 is an example of “motor.” Thesensorless brushless DC motor 31 is formed of a cylindrical rotor 36,and an annular stator 32 that is positioned outward of the rotor 36 witha small gap. The rotor 36 and the stator 32 are coaxial with therotation axis X.

The rotor 36 includes a cylindrical rotor yoke 37 formed of laminatedelectromagnetic steel sheets with magnets 38 embedded in and fixedthereto to be rotatable in unison with the rotary shaft 13. The stator32 includes a stator core 33 formed of laminated electromagnetic steelsheets, insulating coil support frames 35 for covering teeth of thestator core 33, and coils 34 wound around the coil support frames 35.Alternating current is impressed to the coils 34 by power supply from anexternal driver unit 50 described later. The sensorless brushless DCmotor 31 having no magnetic sensor such as a Hall element is configuredto detect a rotating position of the rotor 36 using induced voltagecaused by the coils 34 and switch energization to each of three phasesof windings based on magnetic positional information obtained from thedetected rotating position. The rotor 36 is rotated by repeatedattraction and repellence between the coils 34 and the magnets 38 causedby alternating current, and then the inner rotor 15 is rotated with therotation of the rotor 36.

(3) Structure of Motor Case

As understood from FIG. 1, the pump unit 10 and the motor unit 30 areaccommodated in an inner space of a bottomed, cylindrical motor case 60made of metal such as iron and aluminum. Outer circumferential surfacesof the stator 32, the pump housing 11 and the pump cover 40 are fixed,e.g., welded or adhered, to an inner wall surface of the motor case 60.A groove is formed over the entire outer circumferential surface of thepump cover 40 to receive an annular seal 46. The annular seal 46prevents oil from entering from a gap between the motor case 60 and thepump cover 40. Further, a seal 47 is provided on a side surface of themotor case 60 through which the discharge passage 44 extends, thereby toprevent oil from entering the interior of the motor case 60.

A through hole 62 is formed in a bottom surface of the motor case 60.The through hole 62 is an example of “intake opening.” With thisarrangement, external space of the electric oil pump 1 communicates withan inner space of the motor case 60 in which the motor unit 30 isdisposed via the through hole 62. The inner space of the motor case 60also communicates with the intake passage 43 of the pump housing 11 andfurther communicates with the inscribed gear pump 14 through the intakeport 41 a ahead.

A strainer screen 64 is attached to an outside of the through hole 62 ofthe motor case 60. The screen 64 is a metal mesh filter for catching andremoving foreign substances from oil. This arrangement can keep oil thatis drawn into the electric oil pump 1 via the through hole 62 from anyforeign substances.

A collar-shaped flange 66 that is bent radially outward is provided atan opening end of the motor case 60, and a plurality of through holes 68are formed in the flange 66 along its circumferential direction atregular intervals. The electric oil pump 1 is attached to a wall surfaceof a transmission case 72 via the through holes 68.

[Mounting Structure for Electric Oil Pump]

Referring to FIG. 1, the electric oil pump 1 is fixedly attached to aninner wall 72 a acting as an inner side wall of the transmission case 72via screws 69 extending through the through holes 68 formed in theflange 66. The interior part of the transmission case 72 also acts as anoil pan 74 for reserving oil, in which the electric oil pump 1 islocated under an oil surface 100 and completely submerged in oil. Theoil surface 100 borders on air when oil circulates within a transmission70. The electric oil pump 1 may be exposed in part above the oil surface100. In such a condition, however, the through holes 62 need to bealways located under the oil surface 100 during operation of theelectric oil pump 1. A mounting position of the electric oil pump 1 tothe inner wall 72 a is determined based on an inclination of theelectric oil pump 1 relative to the oil surface 100 when anunillustrated vehicle (motorcar) travels a slope, for example. Acondition in which at least the through holes 62 of the electric oilpump 1 are located under the oil surface 100 during operation of theelectric oil pump 1 is referred to as “submerged in oil” hereinafter.

The driver unit 50 is attached to an outer side of the transmission case72, i.e., the opposite side of the electric oil pump 1 across the innerwall 72 a of the transmission case 72. The driver unit 50 is configuredto supply electric power to the sensorless brushless DC motor 31 of theelectric oil pump 1 for driving and control operations such as driving,rotation, and stop of the sensorless brushless DC motor 31. Further, thedriver unit 50 calculates rotating speed of the sensorless brushless DCmotor 31 based on an input of the induced voltage caused by the coils34, and transmits (outputs) the rotating speed to an upper ECU(Electronic Control Unit) 80. The driver unit 50 includes electroniccomponents such as a microcomputer, a capacitor, a comparator, and aswitching element, which are mounted on a substrate 52. The driver unit50 is attached to an outer wall 72 b, which is the outer side wall ofthe transmission case 72 through legs 54. Power supply from the driverunit 50 to the coils 34 and electric-signal communication between thedriver unit 50 and the coils 34 are performed via a covered cable 56 orconnecting pins connected therebetween through connectors or soldering.Fig. I shows that the covered cable 56 extends through the transmissioncase 72 and the motor case 60. Unillustrated seals are provided inportions of the cases through which the cable extends to prevent oilfrom seeping out to the outside of the transmission 70 or seeping intothe interior of the electric oil pump 1.

[Operations of Electric Oil Pump]

Next, operations of the electric oil pump 1 when actuated will bedescribed hereinafter. Referring to FIG. 1, the electric oil pump 1 issubmerged in oil. Thus, oil reserved in the oil pan 74 enters the motorunit 30 and the pump unit 10 within the motor case 60 through the screen64 and the through hole 62, that is, the motor case 60 is filled withoil even when the pump is not actuated. As electric power is supplied tothe coils 34 from the driver unit 50 in response to an instruction fromthe ECU 80 in this condition, the coils 34 of the sensorless brushlessDC motor 31 are impressed to generate a rotation magnetic field, whichcauses rotation of the rotor 36. The rotation of the rotor 36 istransmitted to the inner rotor 15 of the inscribed gear pump 14 throughthe rotary shaft 13 to rotate the inner rotor 15. This generatesnegative pressure in the pump chambers 17 facing the intake ports 41 aand 41 b. As a result, the oil reserved in the oil pan 74 passes throughthe screen 64 and the through hole 62 and is drawn into the motor unit30. The oil then flows through a gap between the rotor 36 and the stator32 and gaps between the adjacent coils 34 wound around the stator cores33 to reach the intake port 41 a through the intake passage 43. The oildrawn in the pump chambers 17 through the intake ports 41 a and 41 b ispressure fed to the discharge ports 42 a and 42 b, and then dischargedto the discharge passage 44 through the discharge port 42 b. Thedischarged oil is fed to unillustrated parts of the interior of thetransmission 70 and other parts. The fed oil lubricates and cools theseparts, and then flows back to the oil pan 74 to be reserved there. Partof the oil drawn into the motor unit 30 enters between the shaftreceiving hole 19 of the pump housing 11 and the rotary shaft 13 tolubricate the shaft support portion.

In the current embodiment, the oil is directly drawn from the throughhole 62 with the electric oil pump 1 being submerged in oil, and thus isnot required to be drawn from a communication pipe as in a conventionalmanner, as a result of which no piping resistance is generated. In this,it is possible to determine output of power from the sensorlessbrushless DC motor 31 only based on viscosity resistance, which candownsize the sensorless brushless DC motor 31 and provide a moreinexpensive electric oil pump 1.

In the conventional arrangement in which oil is drawn from acommunication pipe, a strainer screen is attached to a distal end of thecommunication pipe submerged in the oil pan 74, and an oil filter, whichis coarser than the strainer screen, is attached to a border between theintake passage 43 of the electric oil pump 1 and the communication pipe.On the other hand, in the current embodiment, the electric oil pump 1 issubmerged in oil when attached to the transmission case 72, and it isonly required that the screen 64 be attached to the outside of thethrough hole 62 to remove foreign substances from the oil, whichdispenses with any oil filter. In this aspect as well, the costreduction for the electric oil pump 1 can be achieved.

According to the current embodiment in which the inscribed gear pump 14has a flow passage arrangement to draw oil flowing within the motor unit30, the inscribe gear pump 14 can draw oil that has high temperature andlow viscosity due to heat generation caused by actuation of thesensorless brushless DC motor 31. This allows the inscribed gear pump 14to smoothly rotate. Additionally, the oil contrariwise absorbs the heatgenerated by the sensorless brushless DC motor 31 when the oilcommunicates through the interior of the motor unit 30. Thus, thesensorless brushless DC motor 31 is not excessively heated and therotation efficiency of the sensorless brushless DC motor 31 is notlowered.

The present invention is not limited to the current embodiment in whichthe through hole 62 is formed in the bottom surface of the motor case60. The electric oil pump 1 may be attached with the through hole 62being formed in a part of the side surface of the motor case 60 awayfrom the pump unit 10 to open downward in FIG. 1 (to be opposed to thebottom of the oil pan 74).

[Control of Rotating Speed of Sensorless Brushless DC Motor]

While the engine is stopped due to a function for turning off the enginewhen a vehicle is temporarily stopped, it is required that thesensorless brushless DC motor 31 of the electric oil pump 1 rotate witha proper rotating speed to allow the electric oil pump 1 to supplyproper oil pressure to the transmission 70. The rotating speed of thesensorless brushless DC motor is calculated at the driver unit 50,converted to a pulse signal of a frequency corresponding to the rotatingspeed, and is transmitted to the upper ECU 80. Referring to FIG. 3, theECU 80 determines a state of motor to be a normal rotation state if therotating speed transmitted from the driver unit 50 is within apredetermined range (A Hz to B Hz in FIG. 3), an unusual high-speedrotation state if the rotating speed is higher than the predeterminedrange, and an unusual low-speed rotation state if the rotating speed islower than the predetermined range.

As described above, the sensorless brushless DC motor 31 has no magneticsensor such as a Hall element and detects a rotating position of therotor 36 using induced voltage caused by the coils 34. Thus, the pulsesignal corresponding to the rotating speed of the sensorless brushlessDC motor 31 is calculated based on a period of the induced voltage. Theinduced voltage caused by the coils 34 is an example of “first signal,”and the pulse signal transmitted to the ECU 80 is an example of “secondsignal.”

Oil pressure of the electric oil pump 1, which is required for supplyingoil to the transmission 70, varies depending on vehicle types orenvironmental conditions such as surrounding temperature. In many cases,however, a range of normal rotation in the ECU 80 (referred to as“normal range” hereinafter) is fixedly determined regardless of theseconditions. Thus, the unusual low-speed rotation state is detected whenthe rotating speed of the sensorless brushless DC motor 31 is lower thanthe normal range even when the electric oil pump 1 supplies required oilpressure. Once the unusual state is detected, the function for turningoff the engine when the vehicle is temporarily stopped is no longeractivated.

In the control of the rotating speed of the sensorless brushless DCmotor 31 in the current embodiment, when the rotating speed of thesensorless brushless DC motor 31 is lower than the normal range of theECU 80 with the electric oil pump 1 supplying required oil pressure tothe transmission 70, the pulse signal is corrected to a signal with afrequency that is determined by the driver unit 50 as falling within thenormal range and then transmitted to the ECU 80. More specifically, thedriver unit 50 corrects the pulse signal of a frequency corresponding tothe rotating speed calculated based on the induced voltage to a pulsesignal with a higher frequency, which is then transmitted to the ECU 80.As a result, the ECU 80 determines that the sensorless brushless DCmotor 31 of the electric oil pump 1 rotates with rotating speed thatfalls within the normal range without detecting the unusual low speedrotation.

The driver unit 50 stores data in the form of table, which data relatesto the rotating speed of the sensorless brushless DC motor 31 in whichrequired oil pressure can be fed to the transmission 70 in response tothe vehicle types or the environmental conditions. When the sensorlessbrushless DC motor 31 rotates with rotating speed greater than therotating speed within the normal range, i.e., rotates with a rotatingspeed outside the normal range and within a predetermined range ofrotating speed outside the normal range, a pulse signal with a frequencythat is determined as falling within the normal range is transmitted tothe ECU 80.

Performing the above control of the rotating speed of the sensorlessbrushless DC motor 31 allows the ECU 80 to determine that the sensorlessbrushless DC motor 31 rotates within the normal range with required oilpressure being fed to the transmission 70 without increasing the outputof power of the sensorless brushless DC motor 31.

2. Variation of First Embodiment

A mounting structure for the electric oil pump 1 according to avariation of the first embodiment of the present invention will bedescribed hereinafter in reference to FIG. 4. Here, like numerals orsymbols indicate like elements or structures both in this variation andin the first embodiment. The descriptions of the same elements orstructures are omitted hereinafter. Unlike the first embodiment, thevariation provides a mounting structure for the electric oil pump 1 inwhich the inner part of the transmission case 72 forms the pump cover40, the transmission case 72 has a recess 76 for receiving the driverunit 50, which recess is concaved inward in a portion where the electricoil pump 1 is attached. Additionally, a cover 78 is attached to therecess 76. The other structures are the same as in the first embodiment.

In this variation as well, the electric oil pump 1 is also submerged inoil, in which oil is directly drawn from the through hole 62 and thusthe output of power of the sensorless brushless DC motor 31 can bedetermined only based on the viscosity resistance of oil irrespective ofpiping resistance. This makes the sensorless brushless DC motor 31compact to provide a more inexpensive electric oil pump 1. Additionally,as the electric oil pump 1 is submerged in oil when attached to thetransmission case, it is only required that the screen 64 be attached tothe outside of the through hole 62 to remove foreign substances fromoil, which dispenses with a coarse oil filter. In this aspect as well,the cost reduction for the electric oil pump 1 can be achieved.

3. Second Embodiment [Construction of Electric Oil Pump]

Next, the electric oil pump 1 according to a second embodiment of thepresent invention will be described in reference to FIG. 5. Here, likenumerals or symbols indicate like elements or structures throughout thefirst embodiment, the variation of the first embodiment, and the secondembodiment. The descriptions of the same elements or structures areomitted hereinafter.

(1) Structure of Pump Unit

In the current embodiment, two stays 18 are formed along an outercircumference of the pump housing 11 with intervals of 180 degrees, eachof the stays radially projecting from the outer circumferential surfaceof the pump housing 11. Each stay 18 has a through hole 68 through whicha later-described screw 69 extends. The stays 18 may be provided inthree or more positions.

The pump cover 40 is provided adjacent to the pump housing 11. In thesame manner as in the variation of the first embodiment, the pump cover40 is machined to the inner wall 72 a of the transmission case 72 to beformed as part of the transmission case 72. The part of the transmissioncase 72 acting as the pump cover 40 is thicker than the other parts andprojected inward of the transmission case 72. The pump cover 40 has theintake port 41 b provided opposite to the intake port 41 a across thereceiving recess 12, and the discharge port 42 b provided opposite tothe discharge port 42 a across the receiving recess 12.

The intake passage 43 extends outward from the intake port 41 b, and thedischarge passage 44 extends outward from the discharge port 42 b. Theintake passage 43 has an outer end submerged in oil reserved in the oilpan 74 to draw oil into the interior (intake ports 41 a and 41 b) of theelectric oil pump 1 by negative pressure generated in the pump chambers17 when the inscribed gear pump 14 rotates. The screen 64 for a strainer92 is attached to the outer end of the intake passage 43 to preventforeign substances present in oil from entering the interior of theelectric oil pump 1. The intake passage 43 is an example of “intakeopening” in the current embodiment.

Two stays 49 are formed along an outer circumference of the pump cover40 with intervals of 180 degrees, each of the stays radially projectingfrom the outer circumferential surface of the pump cover 40. Each stay49 has a threaded groove to receive the later-described screw 69. Thestays 49 are aligned with the stays 18 of the pump housing 11.

(2) Structure of Motor Unit

In the motor unit 30 according to the current embodiment, two stays 39are formed along an outer circumference of the stator core 33 withintervals of 180 degrees, each of the stays radially projecting from theouter circumferential surface of the stator core 33. Each stay 39 hasthe through hole 68 through which the later-described screw 69 extends.The stays 39 are aligned with the stays 18 of the pump housing 11 andthe stays 49 of the pump cover 40.

(3) Structure of Motor Case

Referring to FIG. 5, the bottomed, cylindrical motor case 60 made ofmetal such as iron or aluminum is disposed to receive part of the motorunit 30 (right part in FIG. 5) in the current embodiment. Two stays 61are formed along an outer circumference of the motor case 60 withintervals of 180 degrees, each of the stays radially projecting from theouter circumferential surface of the motor case 60. Each stay 61 has thethrough hole 68 through which the later-described screw 69 extends. Thestays 61 are aligned with the stays 18 of the pump housing 11, the stays49 of the pump cover 40, and the stays 39 of the stator core 33.

[Mounting Structure for Electric Oil Pump]

Referring to FIG. 5, the electric oil pump 1 is assembled by insertingthe screw 69 into the through hole 68 formed in the stays 61, 39 and 18to engage with the threaded groove of the stay 49 with these stays beingaligned. With such an arrangement, the pump housing 11 and the motorunit 30 are integrally formed to provide the electric oil pump 1attached to the inner wall 72 a of the transmission case 72.

In the same manner as in the first embodiment and the variation of thefirst embodiment, the electric oil pump 1 is located under the oilsurface 100 and completely submerged in oil. The oil surface 100 borderson air when oil circulates within the transmission 70. In this, theelectric oil pump I may be exposed in part above the oil surface 100. Insuch a condition, however, the outer end of the intake passage 43 fordrawing oil needs to be always located under the oil surface 100 duringoperation of the electric oil pump 1. A mounting position of theelectric oil pump 1 to the inner wall 72 a is determined based on aninclination of the electric oil pump 1 relative to the oil surface 100when a vehicle (motorcar) travels a slope, for example. A condition inwhich at least the outer end of the intake passage 43 of the electricoil pump I is located under the oil surface 100 is referred to as“submerged in oil” in the current embodiment.

In the same manner as in the variation of the first embodiment, therecess 76 is formed in the outer wall 72 b, which is the outer sidesurface of the transmission case 72, for receiving the driver unit 50.Additionally, the cover 78 is attached to the recess 76.

As illustrated in FIG. 5, the driver unit 50 is electrically connectedto the coils 34 through connecting pins 58. On the side of the driverunit 50, the connecting pins 58 extend through the substrate 52 to besoldered to lands of a wiring pattern. On the side of the coil 34, theconnecting pins 58 are held extending through the coil support frames 35with the coil winding drawn out of the coils 34 along the coil supportframes 35 and bound up to and soldered to the connecting pins 58. FIG. 5shows that the connecting pins 58 extend through the transmission case72. An unillustrated seal is provided in this portion of thetransmission case 72 through which the connecting pins extend, therebyto prevent oil from seeping out to the outside of the transmission 70.

[Operations of Electric Oil Pump]

Next, operations of the electric oil pump 1 when actuated will bedescribed hereinafter. Referring to FIG. 5, the electric oil pump 1 issubmerged in oil. Thus, oil reserved in the oil pan 74 flows into theintake ports 41 a and 41 b through the screen 64 and the intake passage43 even when the pump is not actuated. As electric power is supplied tothe coils 34 from the driver unit 50 in response to an instruction fromthe ECU 80 in this condition, the coils 34 of the sensorless brushlessDC motor 31 are impressed to generate a rotation magnetic field, whichcauses rotation of the rotor 36. The rotation of the rotor 36 istransmitted to the inner rotor 15 of the inscribed gear pump 14 throughthe rotary shaft 13 to rotate the inner rotor 15. This generatesnegative pressure in the pump chambers 17 facing the intake ports 41 aand 41 b. As a result, oil drawn into the pump chambers 17 through theintake ports 41 a and 41 b is pressure fed to the discharge ports 42 aand 42 b, and then discharged to the discharge passage 44 through thedischarge port 42 b. The discharged oil is fed to unillustrated parts ofthe interior of the transmission 70 to generate oil pressure there, andthen flows back to the oil pan 74 to be reserved there.

In the current embodiment as well, oil is directly drawn from the sidesurface of the pump cover 40 into the intake passage 43 with theelectric oil pump 1 being attached to the transmission case 72 whilesubmerged in oil, as a result of which no piping resistance isgenerated. Accordingly, in the current embodiment as well, it ispossible to determine output of power from the sensorless brushless DCmotor 31 only based on viscosity resistance irrespective of pipingresistance, which can downsize the sensorless brushless DC motor 31 andprovide a more inexpensive electric oil pump 1.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a mounting structure for electricoil pump used for a vehicle such as an motorcar.

DESCRIPTION OF REFERENCE NUMERALS

1 electric oil pump

10 pump unit

11 pump housing (housing)

14 inscribed gear pump (pump)

15 inner rotor

16 outer rotor

30 motor unit

31 sensorless brushless DC motor (motor)

40 pump cover (housing)

50 driver unit

60 motor case

62 through hole (intake opening)

64 screen

72 transmission case

72 a inner wall

74 oil pan

76 recess

80 ECU

1. A mounting structure for electric oil pump comprising: an electricoil pump including a pump unit having a pump, a motor unit disposedadjacent to the pump unit and including a motor for rotating the pump, amotor case for housing at least part of the motor unit, and an intakeopening formed in the motor case or the pump unit for supplying workingoil to the pump unit; and a transmission case including an oil pan forhousing the electric oil pump, wherein the electric oil pump is attachedto the transmission case with at least the intake opening beingsubmerged in the working oil reserved in the oil pan.
 2. The mountingstructure according to claim 1, wherein the electric oil pump furthercomprises a driver unit for controlling rotating speed of the motor, andwherein the driver unit is disposed outside the transmission case andlocated opposite to the motor unit across the transmission case.
 3. Themounting structure according to claim 1, wherein a strainer screen isattached to the intake opening.
 4. The mounting structure according toclaim 1, wherein the pump unit includes an inner rotor, an outer rotormeshed with the inner rotor to rotate with rotation of the inner rotor,and a housing for accommodating the inner rotor and the outer rotor,wherein the inner rotor and the outer rotor are made of differentmaterials from each other, and wherein the outer rotor is made of amaterial having a linear expansion coefficient greater than that of amaterial forming the housing.
 5. The mounting structure according toclaim 1, wherein the electric oil pump further comprises a driver unitfor controlling rotating speed of the motor, wherein the driver unitreceives a first signal which is outputted from the motor andcorresponds to the rotating speed of the motor, and outputs the signalto an upper ECU as a second signal, wherein the ECU determines whetherthe rotating speed of the motor falls within a normal range, and whereinthe driver unit corrects the received first signal to a signal fallingwithin the normal range when the first signal indicates that the motorrotates with a rotating speed outside the normal range and within apredetermined range of rotating speed outside the normal range, andoutputs the corrected signal to the ECU as the second signal.
 6. Themounting structure according to claim 5, wherein the first signal iscorrected when the first signal indicates lower rotating speed than thenormal range.
 7. The mounting structure according to claim 1, whereinthe intake opening is provided opposite to the pump unit across themotor unit, and wherein the working oil flows within the motor unit andis supplied to the pump unit.
 8. The mounting structure according toclaim 1, wherein the pump unit includes a pump housing and a pump cover,which are disposed adjacent to each other, wherein the pump housing andthe motor unit are integrally attached to an inner wall of thetransmission case, and wherein the pump cover is formed in thetransmission case.
 9. The mounting structure according to claim 8,wherein a recess is formed in an outer wall of the transmission case,and wherein the driver unit is housed in the recess.